Life indicator for high voltage tubes



Nov. 11, 1958 J. DE GIER ETAL 2,860,302

LIFE INDICATOR FOR HIGH VOLTAGE TUBES Filed June 14, 1955 INVENTORS JOHANNES DE GIER JOHANNES CORNELIS JANssaH A NT United States Patent LIFE INDICATOR FOR HIGH VOLTAGE TUBES Johannes de Gier and Johannes Cornelis Janssen, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application June 14, 1955, Serial No. 515,454

Claims priority, application Netherlands June 28, 1954 8 Claims. (Cl. 324--20) This invention relates to a life indicator for tubes adapted to operate at comparatively high voltages, i. e., voltages of kv. or higher, and more particularly to life indicators for television cathode-ray tubes and transmitter tubes.

When a tube breaks down, it is frequently desirable to be able to determine to what extent that tube has been used, i. e., what performance the tube has given. If the tube is employed constantly, its performance will be proportional to the duration of use; however, if the current strength in the tube has undergone considerable variation during operation, it is of importance to be able to determine how much energy the tube has used or produced. Thus, with a cathode-ray tube, its useful life will be shorter if, during operation, frequent high beam currents were used, than for the case where the current was usually maintained small.

A known life indicator involves the provision on the envelope of the discharge tube of materials or strips which gradually change color due to the heat produced during operation. The magnitude of the color change enables the duration of operation of the tube to be determined. However, this change in color is substantially independent of the extent to which the tube was actually used, since the temperature is only slightly dependent upon variations in the average anode current. Further, such indicators cannot be used in tubes which are substantially unheated during operation, such as cathode-ray tubes.

In accordance with the invention, in electric discharge tubes for comparatively high voltages, and in particular cathode ray tubes, a very satisfactory indication of the energy used by the tubes is obtainable by the provision of an indicator comprising a substance which is sensitive or responsive to soft X-rays. The term sensitive substance as used herein, denotes a substance which upon irradiation by soft X-rays produces a directly or indirectly perceptible change of some form. A very suitable construction involves an X-ray film strip Wrapped up in a light-proof housing and affixed to the outer side of the tube wall. After development of the film strip, the extent of blackening thereof enables a determination to be made as to what part of its normal expected life the tube has already spent. However, as an alternative, use may be made of a strip of paper which is impregnated with chemical substances which change in color on irradiation by X-rays, or a similar substance, for example, an enamel of low melting point containing a high amount of manganese oxide, may be applied to the tube wall or to one of the electrodes. When such latter construction is employed, care must be taken that the sensitive substance is not struck by electrons during normal operation of the tube.

The invention is based upon the realization that, in cathode-ray tubes and transmitter tubes, soft X-rays are produced due to the fact that electrons impinge on a collector electrode at high velocity. In a cathode-ray Patented Nov. 11, 1958 tube, the fluorescent screen acts as the collector electrode. In such tubes, therefore, the sensitive layer may be applied to the cone of the envelope, for example, in the form of a strip extending in the direction of a generatrix of the cone. The parts of the strip which are more remote from the screen are struck to a smaller extent by the X-rays emitted from this screen, so that the blackening gradually decreases in the direction from. the screen to the neck of the cone. By arranging shielding members, e. g., metal plates or rings, which absorb X-rays between the cone wall and the strip, skiagraphs may be obtained in which the variation of the blackening therein enables a quantitative determination to be made of the extent to which the tube has been used. In a tube having a metal cone, the sensitive substance may advantageously be arranged on the inner side.

The invention will now be described more fully with reference to the accompanying drawing, in which:

Fig. 1 shows an indicator according to the invention mounted on a cathode-ray tube;

Fig. 2 shows an indicator in accordance with the invention.

In Fig. l, a cathode-ray tube comprises a fluorescent screen 1, a cone 2 which in this case may be. made of glass, and a neck 3 housing an electrode system. To the outside of the cone 2 is cemented an Xray film strip 4 wrapped up in black paper, and metal discs 5 are mounted between the film 4 and the cone wall 2. During op eration of the tube, which normally uses an anode voltage of, for example, 15 kv., the strip 4 will be struck by soft X-rays generated at the screen 1, most intensely at the end adjacent the screen 1. The longer that the tube is operated, the further will the blackening extend in the direction of the neck 3. The metal plates 5 enable an ascertainment as to how far the blackening has proceeded. In the embodiment shown, provision is made of ten plates 5 and, and may be seen from Figure 2, the developed film strip shows that the tube has used approximately 60% of its normal life, the plates 5 here serving as markers or indicia to facilitate the observation. Theintensity of the X-radiation is dependent not only on the voltage, but also on the brightness of the image, i. e., of the beam current strength, so that a more intense use of the tube causes an increase in the blackening. On the developed film strip, the position of the articles 5 is recognizable by the areas 6 which are blackened to a lesser degree.

Hence, when tube failure occurs, the use of the invention enables one to accurately ascertain whether or not a manufacturing defect is responsible. In addition, fraud can be established, for the film strip may be entirely covered by a coating layer which is applied to the outer side of the glass cone, for example, a lacquer layer or a metal layer, so that removal of this layer will inevitably leave traces. The metal plates 5 may be shaped in other forms; they may, for example, be designed as a strip containing notches or having numerals punched in it.

While we have described our invention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In combination, an electric discharge tube adapted for comparatively high voltages and producing soft X- rays, and a life indicator comprising a substance sensitive to soft X-rays whose appearance changes in accordance with the intensity of incident X-radiation, said life indicator being associated with said tube and being arranged so that some of its portions receive more X-radiation from the tube than others of its portions, whereby the extent of appearance-changes indicates the extent of use of said tube.

2. Incombination, an electric discharge tube containing electron-producing and electron-receiving electrodes adapted to operate at relatively high potentials such that the impact of electrons on said electron-receiving electrode generates X-radiation, and means arranged near said electron-receiving electrode and responsive to X-radiation for indicating the lifetime of the tube, said means including an element whose appearance changes in accordance with the intensity of incident X-radiation and arranged so that some portions of it are nearer the electron-receiving electrode than others of its portions.

3. T he combination set forth in claim 2, wherein the tube is a cathode-ray tube, and the electron-receiving electrode is a luminescent screen.

v4. In combination, a cathode-ray tube comprising an evacuated envelope and electron-producing means and adapted to have comparatively high potentials applied thereto thus to produce soft X-rays, and means coupled to said tube for indicating its lifetime, said indicating means including a soft X-ray responsive member arranged in the evacuated envelope in a position Where it cannot be impacted by electrons during the normal operation of the tube.

5. In combination, a cathode-ray tube comprising a conical envelope portion and adapted to have comparatively high potentials applied thereto thus to produce soft X-rays, and means coupled to said tube for indicating its lifetime, said indicating means including a soft X-ray responsive member mounted on the conical envelope portion.

6. The combination as claimed in claim 5 in which the indicating means comprises a photographic film strip in a light-opaque enclosure and extending in the direction of a generatrix of the conical portion.

7. In combination, a cathode-ray tube comprising an evacuated envelope including a glass conical portion and adapted to have comparatively high potentials applied thereto thus to produce soft X-rays, and means coupled to said tube for indicating its life, said indicating means including a soft X-ray responsive film strip mounted on the outer side of the glass conical portion, and an X-ray absorbing member mounted between the glass conical portion and a portion of the film strip.

8. The combination as set forth in claim 7 wherein a plurality of equi-spaced X-ray absorbing members are provided between the glass conical portion and the film strip and extend parallel to the latter.

References Cited in the file of this patent UNITED STATES PATENTS 1,077,479 Klein Nov. 4, 1913 2,381,261 Cota Aug. 7, 1945 2,496,218 Kiefier Jan. 31, 1950 2,509,766 Gross May 30, 1950 2,624,011 Stern Dec. 30, 1952 2,722,519 Otley et al. Nov. 1, 1 955 FOREIGN PATENTS 17,666 Great Britain Sept. 24, 1903 2,432 Great Britain Aug. 11, 1910 792,092 France Dec. 21, 1935 

